Radar system and display



July 5, 1960 F. D. COVELY 3RD., ETAL RADAR SYSTEM AND DISPLAY 5 Sheets-Sheet 1 Filed Deo. 31, 1954 A mmf@ INVENTORS fm1/m www@ zffrf fm/W@ y gzzazf Hmm/fr July 5, 1960 F. D. covELY 3RD., lETAL 2,944,253

RADAR SYSTEM AND DISPLAY Filed Dec. 5l, 1954 5 Sheets-Sheet 2 Q www? @QN m m im ,wl l* Nw @wmwmwm AGES* N .KN

F. D. covELY 3RD., ETAI 2,944,253

RADAR SYSTEM AND DISPLAY 5 Sheets-Sheet. 3

Jury s, 19Go Filed Dec. s1, `19,54

July 5, 1960 F, D COVELY ;3R|:J y ETAL 2,944,253

RADAR SYSTEM AND DISPLAY Filed Dec. 3l, 1954 5 Sheets-Sheet 4 July 5, 1960 F. D. covELY 3RD., ETAL. 21,944,253

RADAR SYSTEM AND DISPLAY 5 Sheets-Sheet 5 Filed Dec. 3l, 1954 E www y m SQ v1 @WIIL WS l No NSK ly selected for `that target. a

` 2,944,253 RADAR sYsrsM AND DISPLAY Frank D. Covely 3rd, Haddoniield, and Lester E. Hainiug, Audubon, NJ., assignors `to Radio Corporation of America, ac'orporationof Delaware t rues nec. s1, 1954, ser. N0.479,is1 27 rc1-aims. (ci. 34a-5) This invention relates to the designation of target and the initiation of the automatic tracking operation in automatic track-while-scan radar systems.

w As the numbers of `aircraft using the. air `lanes has `ncreased, the problem of traiiic controlat airportshas be,- `come acute. To aidin the automatic surveillance of trac at airports, automatic-track-while-scan (ATWS) radar systems have been developed. These systems automatically track, and supply electrical position data with respect to, a plurality of moving targets. ATWS radar systems `'are also useful` in the surveillance of ship traflic f aten-t Patented July 5,' i960 ice for initiating the automatic tracking process of an ATWS radar. t

An object of this invention is to provide in an ATWS radar improved .and simplified means for selecting a set of stores to be associated with a particular target.

Another object of this invention is to provide in an ATWS radar improved and simplified means for inserting in the target stores the preliminary target data required to initiate the automatic tracking operation.

Yet another object of this invention ilstto provide an improved indicating system which affords a composite display of thev indications from a pair of display devices, in which composite display corresponding indications rom cach display `device are superimposed and in which the superimposed indicationsand the non-superimposed indications are readily distinguishable from each other. AA further object of this invention is to provide an operator with a quick and simple means for determining which targets on a radar display tube are being automatically tracked by the radar. t

The foregoing objects and advantages of the present i inventionar'e accomplished by means ot a combination in port areas and in the 'designation ofV targets to military l V"fire-control systems.` 1

= In ATWS radar systems, a'plot of the position, with respect tothe-radar, of targets Whose echoes are received bythe` rotating radar antenna is usually displayed on the screen of, a P.P.I. (plan-position-indicator) display tube, and, in addition, analog voltages corresponding 'to the cartesian coordinates (i.e., the X--Y coordinateslof the positions of selected targets are supplied to sets ofstorage circuits. In a typical system, one set of stores is associated with each selected target, and one X-storage circuitand one Y-storage circuit comprise one set. The stored analog voltages may be used for various purposes, suchas automatic. orientation of anti-aircraft artillery, synthetic display of one or more targets', etc. 1

To maintain the accuracy of such position data, l,it is essential periodically.r to correct the stored analog voltages inlccordance with changes in the positions ofthe targets; v p "This .is accomplished once'per antenna scan` by resolving each received target echo signal into the X- and Y- coordinatet'analog voltages corresponding to the .location of'the target.` The new coordinate analog voltages of leach target are then used to correct the set of stores associated With that particular target. This,- isdone by automatically comparingfeach new set"oftcoordinate analog voltages with the: voltages` `stored in all' sets of X-Y stores, selecting the `set of storeswhose stored voltage most nearly correspond with the new voltages (normally the same set of stores associated with the target during the previous scan) and altering that set of stored voltages to correspond to the new set of coordi. nate voltages (new position data). This automatic comparison and correction of the stored data with the new data comprises the automatic tracking feature of ATWS radar systems. v l

VBefore the automatic comparison and correction feature'can come into operation, however, each set of stored voltages'must approximate a set of `corresponding analog voltages offa "corresponding` particularftargetll In other vv'ords, there 'mst be "an initial selection foreach diiferent target to be tracked of a different set of X-Y stores,

Y and the set of analog voltages corresponding to each different `target must then be `inserted in the'storc previous- This invention lprovides a comparatively simple means fof apparatus which permits an ATWS radar operator to ascertain at a glance whether or not targets are being tracked. t p

'I'he operator watches a superimposed image comprised of theimage from a `radar display tube, saidV image being transmitted through a dichroic mirror, and the image from a `monitor display tube, said image. being reflected fronrthe` dichroic mirror. The optical arrangement is such thatthescreens of the display tubes are perpendicular to each other and the dichroic mirror is located between the two `screens at an angle of.45 degrees to each. Since a dichroic mirror transmits light ofone color which is ldiiierent from the color of the light which it reilects, the radar image can readily be distinguished from the monitor image-eg., theradar indicationsmay be blue andthe monitor indications may be red.

When the'operator observes a blue indication, he knows that the target it represents is untracked. He then moves the handle, or lever, of a joystick mechanism by means of which direct-current voltages which correspond to the rectangular coordinates of the location of the target can be obtained. The joystick mechanism comprises a lever movably coupled to a Vpair of orthogonally disposed shafts and` capable of rotating-the shafts aboutV their longitudinal axes. The shafts 4are attached to the rotating arms of potentiometers which provide direct-current out- Vput voltages proportional to the displacement of the joy- These voltages areinserted inV a set of store circuits,

which set `is thereafter associated With that particular target.

Once these voltages have been inserted in the stores, the .automatic tracking featuresof `the ATWS radar become operative and the operator can turn his attention 4to another untracked target. t

I Thus, the automatic tracking of radar targets is initiated by operation offa joystick mechanism in conjunction with die'rentiation by means of color diiferences between the radar tatfget indicationsrand the'superimposed monitor indications derived from the joystick mechanism.

The invention will be described in greater detail with reference to ,the accompanying drawing in which similar Vreference characters `apply 'to similar elements, and in which:

Figure 1 is a block and-schematic circuit diag'r'arnof a system which will store and correct target position data provided by a radar set;

Figure 2 is a diagrammatic representation of a'negative analog pulse;

Figure 3 lis -a schematic diagram of a circuit which can be employed to provide negative analog pulses;

Figure 4 is `a block circuit diagram of a system in accordance with this invention which permits an operator to initially select targets to be automatically tracked thereafter by `aneATWS radar; Y. 'Y Y Figure 5 is a diagram of thejoystick mechanism including a 'schematic of .thef Iassociated potentiometers;

Figure 6 is a block .diagram of a systemin accordance with this invention in which apparatus is included for indicating which 'stores are( being utilized;

Figure 7 is a schematic diagram of a coincidence circuit vand a rectier-lter circuit which may he employed in the stores-utilization indicator shown in Figure 6, 'and Figure 8 is a block and schematic circuit diagram indicating the connections to the four-pole, rotaryswitch sampler employed in the embodiment illustrated in Figure 6. i Pulse for'mer Referring-to Figurel-I a typicalembodiment of the invention includes 'a system'v for correcting position data obtained by a radar set.4 'Ihe radar equipment may, for example, comprise a pulse-type search radar delivering target range and azimuth datanand presenting this data in polar coordinates on a plan-position-indicatoa' (P.P.I.) displayscope. Q

Atimer 150, which may be a blocking oscillator or other pulse-generating circuit, delivers trigger pulses to thetransmitter 151 which generates Ihigh-power pulses v of high-frequency electromagnetic energy. These pulses are applied lthrough va duplexer 152, which may -be a gaslled, transmit-receive switch, to the antenna 153, which v radiates the energy into space. The Aantenna is vrotated azimuthallyby means of the antenna drive mechanism steeply rising front and a constant amplitude, so that'the circuits which -are intended to respond to,. or ybe, synchronized by, the stimulus of lthe echo pulse will be actuated in a positive manner which does not vary from pulse to pulse.

Range resolver The range sweep voltage, or range sawtooth, is a sawtooth voltage supplied to the sweep deflection coil 157 (see Figure 4) of an electromagnetic cathode-ray display ftube 90 to sweep the electron beam radially outward from'the 'center of the display tube to its periphery in time synchronism withfthe radiated pulse. The position of the electron beam at any given instant relative to its center or zero position corresponds to the distance the radiated pulse has travelled from the radar antenna 153. Since the position of .the electron beam depends upon the` amplitude of therange sawtooth voltage at that instant, the distance, or range, of the radiated pulse (and, therefore, of any target it strikes) can be determined from the amplitudeof the range'sawtooth Iatthat instant.

The range sawtooth is generated yby applying. a trigger pulse from the timer A150 to the range sawtooth generator 156, which may be any one of anumber of well-known circuits which generate linear sawtooth voltages. Y

To completely locate the geographical position of Vth radiated pulse in relation -to the radar `antenna 153, it is also necessary to take into account the azimuthal position of the radiated pulse, which in turn depends on the i azimuthal rotation ofthe radar'antenna153. The "re-V suit-ant scan is called a P. P .I. '-(planpositionindicator) Scan.

The process of completely 'locating the geographical" position of the radiated pulse is .accomplished'by iapplying the range sawtooth to a' range resolver 12 which separates it into two component sawtooth voltages, `for example, an east-west component hereinafter called the X- sawtoothV 55, and' ahorth-sOu-thV component hereinafter called the Y-sawtoofth 56. ''Ihe outputs the range re' solver 12 are synchronous sawtooth voltages 55` and 56, the relativearnplitudes of -which'yary the vangle of rotation of the radar antenn'axy f Analog pulse generator Y bar 17, respectively, and then. coupled to the VX-analog l pulse generato-1.'v 14 and Y-analog pulse generator l15,

respectively.

An analog voltage dehed herein as a voltage 1 whosev amplitude represents some other quantity. Thus, 1 at any given instant, the amplitudejo- Vthe Y)t-sawtoothn voltage 55 represents the east-west geographical position of a target reecting :2t-transmitted` pulse with respect to the vlocation of the radar antenna #153,' andptherefore, the X-sawtooth voltage S5 is lan analogV of the eastJwest geographical position of saiditargetiat that instant. The

X-sawtooth voltage ,55' is hereinafter interchangeably referred to as the X-analog voltagel `55. A negative Vanalog pulse is deiined'herein' asa pulse whose amplitude measured from zero voltage isthejnega: tive of somel analog voltage. Thus,in Figure 2, a. nega-,f tive analog pulse 57 is shown, having anamplitudeNA which is the negative of the positive analog ,voltage180 v indicated by the dotted line, theV amplitude of which is indicated by the letter A. It willibe noted that, inzthisy particular case, the base line 82 of the pulse 57 does1not negative VVthan the vamplitude NA of the negative analog later.` Continuing with Figure Vl,`only the parts of the system concerned with operations upon the'X-analog voltage,V

or X-sawtooth, willbe -described in detail, s inc'efthe'parts concerned'with operations ,upon the Y-analog voltage, or

l' Y-sawtooth, are similar in construction and function.

A circuit for forming such a negative. analog pulse is Vshown in Figure 3.. The analog voltage, the X-sawtooth voltage 55 fromV the X-bus 16, is impressed on the control grid of'an electron tube 60 operating as an amplier with a gainrof` approximatelyunity by virtue of the relative limpressed sawtooth 55. A,D.-C. restorer circuit com prising condenser 63, diode 64, and resistor Y establishes gronfd potential, or zero volts,ras 'abase voltage from which each negative exclusion 0f the`A sawtoothl originates.'

This Vwave 86 is then impressed upon. acathodefolloweitube 67 which operateswithout plate Voltage mosgrofth time. Y

Thegrid current of the cathode follower tube 67` i limited by grid resistor 66,Y and the'k cathodejs returned through resistor 6,8 to anegativefsupply' voltagewhich Refer-ring still'to Figure l, the and Y-sawteeth 5 5f` and 56 are impressed upon the X-bus bar 16 and Ybus geraete establishes the base line 82 of the negative analog pulse 57 shown in Figure 2. The pulse itself is formed by applying plate voltage to the cathode follower tube 67 at the proper time, this action being accomplished by means of a delay-line pulse generator stage 72 which is triggered on by pulses 87 from the pulse former 13 (see Figure '1) and is cut-oit by the removal of its plate voltage upon termination of the pulse generated by the delay line 73. Thus, the amplitude NA of the negative analog pulse 57 which is obtained across cathode resistor 68 corresponds to the value of the X-sawtooth at the instant an echo pulse is received, and therefore corresponds to the X-component of the geographical location ofthe radars target. This negative analog pulse 57 is then impressed upon the Xp-bus 18. t

The manner in which a pulse is formed bythe gas tube 74 land the delay line '73 in` conjunction with the timing pulse fromV the pulse former 13 is explained in Waveforms, vol. 19, 'Radiation Laboratory Series, pages 239-` The X-sawtooth voltage 55 is coupled from the X-bus` 16 tothe X-analog pulse generator 14, whose output, negative X-analog pulses 57, is impressed upon the Xp-bus 18. Thus the value of the X-analog pulse 57, measured from zero, is indicative of the X-position of the target, the echo from which initiated the formation of the X- analog pulse 57.

Store circuits ,l It will be assumed that the radar is in the process of tracking a target and, therefore, Athat the X storage condenser r32of a lvlillerintegrator of store circuit 31 has tube 31 with respect tothe grid, or the charge stored in Y the condenser 32, is then an analog of the X-component ofthe position of the radar target, and is impressed upon one of the horizontal plates ofthe comparator'tube 21,

while the/Xesawtooth 55 is impressed on the other.

A, Comparison device (comparator) The comparison device, or comparator tube 21, comprises an evacuated electron beam tube including an electron gun with its associated controlgrid, and accelerating and focusing electrodes, all of which are represented in schematic form in Figure l by a cathode 22. The comparator tube 21 also includes two pairs of orthogonal deilecting plates 2?, 24, 25, and 26, a cup-shaped collecting electrode 27 having an aperture in its base, and a target electrode 23 located adjacent to the aperture in the collecting electrode (cup) 27. The analog voltages derived from the X- or Y-storage tubes 31 and 37, are applied to deecting plates 25, 23 respectively in each of the opposed pairs of plates. The other plates 2-4, 26 in each pair are respectively provided with the sawtooth voltages 55 and 56 on the X-bus 16 and Y-bus 17. In the particularembodiment illustrated in Figure 1, the X-voltages 55 and S6 are coupled to the horizontal pair of deilecting plates 24 and 25, although they may be 'coupled to the vertical deilecting plates 23 and 26 if so desired. s Y

During the major portion of the antennasrotation, the amplitudes of the X- and Y-sawteeth voltages 55 and will d iier widely from the anode voltages of the Miller `integrator tubes 31` `and 37. 'I'he electron beam from the cathode of the comparator, or gating, tube 21 will, therefore, be deflected, striking the cup 27 and passingto ground "through resistor 29 connectedl thereto.

Variable-current tube 34 is a tetrode biased by a combinatiton of two voltages. The first is the voltage across resistor 29, which is the result of the current ow from the negative supply voltage to ground through resistors 51, 5o and 29, andthe current flow through resistor 29 alone due to the electron beam from the comparator 2'1. The |second is the Voltage tapped off the voltage divider formed by resistors 40 `and 41, on the highpotential end of which isfimpressed the voltage from the-X-store con.- denser 32 andon the lloyv potential end `of which is impressed the negative potential of theb'ase line of the X-analog pulse. Y A

Constant-current tube 33' whose plate .is in series with the cathode of variable-current tube 34, is a pentode also biased by two voltages. The rstof these is applied to the control -grid and is the-voltagel across resistorsv 50 and 29 of the voltage divider` comprising resistors 51, 50 and 29. "the second is the negative supply voltage and is coupled to the suppressor grid through resistor 52.

The biasing ofthe variable-current and constant-current tubes 36 and 35 associated with the Y-store 37 is accom` plished `in a manner similar to that described above for tubes 34 and 33 associated with the X-store 31.

As the radar antenna 153 sweeps toward the area in which the target was previously located, the amplitudes of the X- and Y-sawteeth S5 and 56 approach equality with the amplitudes of the stored. voltages of the Miller integrator .tubes 31`and 37. 'The electronbeam then experiences very little deilecting potential and passes through the'hole Vin the centerof the cup Z7 to the grounded target 2S. ,The `previous bias acrossresistor 29, due to the action of the electron beam, disappears, leaving the voltage on resistor 29 only slightly negative. The diodes 48 and 47 then cease to conduct leaving the variable-'current tube 34 biased beyond cut-off only by the negative voltage that forms the base ofthe X-analog pulse 57, andconstant-current pentode tube 33biased beyond cut-oil only by the negative voltage coupled to i its suppressor grid through resistor 52. At` this time,

constant-current tube 33 is conduct-ing some screen grid current, but no plate current.l Y

Now, as theiradar--` antenna `151i sweeps across the target, au echo pulse is received. The re-formed echo pulse is coupled to the `suppressor grid of constant-cur- 4'rent tubel33 andraises it `above cut-oit. The function of constant-current tube 33is to conduct aj constant, pretermined value of current during the time anV echo pulse isbeing received. The' negative bias on'its sup-- determined current will be maintained through constantcurrent tube 33 during the time Vthe echo pulse is being received.

Simultaneously with the impressing of the re-formed echo pulse on the suppressor grid of constant-current Atube 33, a negative X-analog pulse 57 is impressed on bus 18 and thence on resistor till.` While these pulsesV persist, the potential on the control` grid of variablei current tube 34 is the resultboth of the oldv analog voltage carried in store `and the new negativeV analog voit- Y age on `bus 18. Thus,'the voltage on the grid lof 341 varies in proportion to the ditferencerbetween 'the stored and the true analog voltages. Thisy difference is `a measure ofthe correction that must be made. fl f1 Thus,` when .the location of the` targetV remainsy changed, Aand variable-current tube 34 conducts the same amountof current-as constant-.current tube 33, Vno current will `flow into the AMiller integrator storage circuit, which-isfeffectivelyin` shunt withv constant-current tube 33, and there will be no change in the quantity of charge stored irl-storage condenser 32.

However, if the position of the target has changed 'since the last sweep: of the radar antenna 153, the value of the X-analog pulse 57 will be diierent from the value of the anodevoltage of the Miller integrator tube 31. A net voltage,either positive or negative from its previousvalue, willnow exist at the control grid of variablecurrent tube 34, causing it to conducteither. more or less current than ,constant-current tube 33. Under these conditions, acurrent willilowV into or out of storage condenser v32, correcting the amount of charge stored in the condenser until it corresponds'to the new X-position 'of' the target as indicated Iby the valueof the negative X-analog pulse. 57.V Y 'j Q Thesmall rheostat 46 in the cathode of the constantcurrent tube 33 is provided `so that the currents flowingfthrougn tubes'33 and`34 mayl be'adjusted for equality when the voltage on the grid of tube 34 indicates that no correction isneeded. Y l

In the description of` the system, the scale of the stored voltage on the anode of the Miller integrator tube 31 was assumed to be equal to the scale of the negative X-'analog pulse voltage 57, and resistor 4i! was assumed to'be equal ,to Yresistor 41.. l-hese voltage scales may be different, provided that Yresistors 40 and 41 are properly proportioned and the base value of the negative analog pulse 57 is suicient to keep variable-current tube 34 biased beyond cut-cli? `between pulses. Y The parts of the system concerned with the correction of the Y-analog voltage v on the storage condenser 38 kare the Miller integrator tube 37, the constant-current tube 35, the'variable-current tube '36, and their associated components, all of whichcorrespond respectively to Vthe following X-analog components: the Miller integrator tube 31, the constant-current tube 33, the variable-current'tube 34, and their associated components.`

n It is to be understood, o f course, that a positionstore circuit, which comprises all of the components to the right ofthe bus bars in Figure l, `is required for each targetvwhi'ch is to ybe tracked, and that if it is desired to store data with respect to more than one target,

' additional position-'store circuits lmust be added to the system.

' kTarget designation mechanism totheincoming X- andYA-analog pulses, recurrentV periodic correction .of the stores automatically results. The

`problem Ais toinitiallyassociate a set of stores with a specic target and insert theproper analog voltages corresponding-to theposition of that specific target.

VReferring 'to Figure 4, .the outputs of all stores are coupled to the sampler 94. The invention includes a plurality of sets of stores but since they are all substantially identical only a single set, comprising Xl-store 31 and Yl-store 37, is illustrated. The sampler 94 may be a high-speed, double-pole, multi-contact, rotary switch, or an 'electronic switching circuit. lf a rotary switch'is employed as illustrated all X-stores are coupled tov one set of contacts 158,159, la, and all Y- yst'cvrres to the other set of contacts 161, 16,2, 163 the X- Y and Y-stores of a single set being, respectively, coul pled to identically-positioned stations, or contacts, on the poles .1641t5s Although onlyV three sets of contacts A.of the switch` tothe X- Vand Y-deflection plates,V respectively,l of the monitor display device 92, which may be a cathode-ray display tube. Theoperating Vvoltages of the monitor display tube 92 are suchthat the-electron beam is operativeY at all times and forms aspot in the' center of the screen of the monitor ,display tube 92 when zero range analog signals are applied from the X-Y stores, as explained subsequently. in connection with the operation Vof the coordinate resolver 93.

- The monitor display tube 92 and the radar display tube 90, f011 which the detected video output of'the receiving circuits 155 is displayed, are arranged-at right angles to .through the dichroic mirror 91 and somelight from the monitor display tube 92 is reflected from the dichroic mirror 9,1 to the eyeof the operator, the optical 'arrange-Y mentof the tubes and mirror being such that target indications on the monitor display tube92 are Vsuperposed upon their counterparts on the radar display tube 90.

However, light coming to the' eye of theobserver from the radar display :device 9i) has ajdiierent color (e.g.;

blue) than light from the monitor display device 92 (e.g.,

red). j

When the radar antenna 153 first picks up a target, it is displayed only on the radar display tube and appears blue to' the observer. If this target were being auto,-

matically tracked by theradar, coordinate analog-.voltlages corresponding to its `position would be stored in a Y set of X- and Y-stores and a .target vindication would appear on the monitormdisplay tube 92. The dichroic mirror 92 imparts a red color to this target indication, 'but it is superposed upon the blue target indication of the radar, display tubeV 90 and the combinationV iswhite to the eye of the observer. Thus, when the observer sees a white indication, he knows that the target is being automatically tracked, but when he sees a blue indication. he knows that coordinate analog voltages for'the target must beinserted in a set of empty X- and Y-stores,

VThe observer then moves the joystick handle 300 '-(Vsee Figure 5) sothat a target indication appears onv monitordisplay tube 92, and continues to move the joy,- stick handle 300 Vuntil this target indication, 'which appears red to him, is superposed upon the original blue .target indication. The ATWS 4radar then tracks th target automatically.

' Coordinate resolver Ihe coordinate resolver isa device by? means of 'which Yfurnishes X- and Y-rectangular coordinate voltages in Iaccordance with the position of the joystick handle 300 is illustrated. The shafts 305 and 304 are supported by'Y four shaft supports 306 mounted on a base (not shown).

The joystick handle 300 is separated into two parts by y a yoke 301, to which the two parts are afxed. The lower part of the handle 360 rides in a groove between the tracks which form the X-shaft .linkage 316.V If the orientation of the X-s'haft 3415 is north-southV andV that of the Y-shaft 304 is east-west, the lower partof the joystick handle can move in a north or south direction in the grooveof the X-shaft linkage 316. Y

The joystick handle 3190 may also be east-westdirection by rotating its Vyoke 301 arounclfz moved in the pair of pivot dov/els 302 afxed -to` the Yshaft coupling block 303 and extending through the yoke 301; Rotating the handle 300 in the east-west direction rotates the X-shaft 30S, to the end of which a slip ring 313 is at- 'tached.y 'Ihe contact arm 308 `of a potentiometer 307, the output voltage of which is proportional tothe angle of deviation `of the handlett) from its vertical position, increasing in positive amplitude as the handle 300 is 'moved from its extreme westerly position to its extreme easterly position.

Similarly, movement of the handle 100 from south to north rotates the Y-shaft 304 and furnishes an increasing positive voltage from the Y-shaft potentiometer 310. The output voltages are taken :from brushes 314 and 312 which contact the slip rings 315 and 313 affixed `to Lthe Y- and X-shafts 304 and 305, respectively. The X- andl Y-outputs are respectively` coupled ithrough a switch 95 to the `anodes of the X'- and Y-stores of one of the sets of stores (see Figure l). The switch 9Sis a `fourpole, multi-position, manually operated switch.. In

each position there arefour contacts: one connected' to A the anode of an X-store tube;` one to thefgrid of `the same .tubeyone `tothe anode `of theY-storetube 'associated lwith said X-store tube as a set; and one `to the grid of the Y-store` tube. Each set of tour contactsiscoupled to a I.. Thusglthe AX'- and Y-shafts Vmay `becomparedto the X- and Y-axes of a rectangular coordinate plot, and the ljoystick mechanism is a means of resolving the location ofthe top section of the joystick handle `300 with respect to the axes into:X andY-coordinate .analog voltages.

4,It may be noted that inV the: particulantype of joystick mechanismindicated in this embodiment the lever can be The operator selects a set of X- and Y-stores by operating the switch 9S. `He then depresses the pushbutton switch 320 and moves the joystick handle 300 to the correct position as previously explained.` If any charges have been retained in those stores from a previous use, the voltages now applied to the grids and anodes of the stores correct them to the Values now desired. The operator then releases the push-button switch 320 and moves switch 9S to a neutral position. Automatic tracking is then initiated.

It is to be noted that other means, such as a pair of independent potentiometers having their contact arms connected to ordinary knobs, may be employed in place of a joystick mechanism 93. The operator would then use one of his hands to operate one knob and the other hand to operate the other knob.

Busy store-empty store indicator In order to prevent the insertion of data for a new target in a store that isbeing utilized vto track another target, it is desirable to provide apparatus that will indicate which stores are, and which stores are not, being utilized at the moment.

moved directly to'the desired position-thns, if the lever fis in a vertical. positionxat theorigin of the X-Y coor` s dinate axes, itmay, for exampl`e,"be moveddirectly along the 45 line bisecting the` angle between the X-Y axes, or in any other desired path. A' 1 i y As aconsequence of the circuit arrangement and constants of the X` `and Y-storesl` and 37, the stored analog of .the X-component of` the `position of a target ranges from O volts `ic` r".thernost westerly position to appro imately +100 volts: for the most easterly position, with Azero range being represented b yapproximately +50 volts. Similarly, thestored analog 'of the Y-cofmponent of the position of v4a target ranges from 0 volts for the most 'southerly position to approximately v-l-lOGvolts for the `most northerly position, with Lzero range being represented by approximately -l-SOfvolts. This necessitatesvgrounding the potentiometers 337 and 310 at the points shown infFig. `5, so that the outputs from the potentiometers 307 and 310` vary from 0 volts to approximatelyl-IGO volts as the joystick handle 300 is'moved from its mostwesterly (or southerly) positionto its most easterly (crnortherly) position. .t

Furthermore, in order to. establish the .aero'rang'e position lof the electron beam Yofthe monitor display device 92 `in the center of itsf'screen, a positive voltage equal toapproximately 50vo`lts must be appliedto the pair of `deflection plates `on which signalsfrom the sampler 94 are not impresed (Fig. 4).

s. The joystick handle 300 also contains a push button switch 320. This switch 320 has `two poles which are coupled to the contact arm of a potentiometer 323. Oneterrninal 324 of this potentiometer` 323 is coupled to a `source of direct-current voltage more negative than that `to which the cathodes of the Miller stores tubes 31 and `37 are coupled. The moving arm of thepotentiorneter 323"is adjusted so that the voltage tapped oir is equal to the grid Voltage required to afford zero rangeontput voitage from the stores 31 'and 37. The output contacts of thepush-button switch 320 `are connectedby means of 'ilexibleleads 321 to a terminal block 322 and thence 'through the switch 95 to the grid electrodes of the set of t X-and Y-stores selected by the switch9`5. i

circuit 98 is then rectied and filtered in the rectiiier-iilter circuit 99; The'` output of rthe rectiiier-lt-er circuit 99` is then impressed upon the proper contact 267 of a third po1e`273` of `the sampler switch 130 (seeFigure 8 for detail of sampler'180) and` when contact is made bythe moving arm of the sampler switch 180 with the contact 264 corresponding spatially to those of the X-Y stores, the output of the rectier-iilter circuit 99 is applied to an amplifier 100.

The sampler switch 18u is a four-pole, multi-position, high-speed rotary switch similar to the two-pole rotary switch 94 employed in the embodiment of the invention illustrated in Figure 6. Again, there are at' least as many positions as there are sets of X--Y stores.

The output of the amplier 100 is impressed upon the proper contact 264 of a fourth pole 272 of thesampler .SwitchV 180 and thence? to a lamp 101, which may be a indicates to the operator that the stores with which it isassociated arebnsy at that moment. Y

If, as is possible, the radar fails to track, or loses,

the target, the lamp101 no'longer lights. `The observer `then applies a direct-current voltage'to the anodes` of the X--Y stores 31 and 37 through contacts 103 of a four-pole, three-position manual switch 104, thereby removing from the monitor display Atube 92. the target indication associated with that set of stores.

Thus, when a new target appears, the observer is aware that the X-Y stores 31 and 37 are available since` the lamp `101 is unlighted and the manual switch 104 is in the lixed voltage position C (connected to the iixed voltage" contacts 103). To insert the coordinate analog voltages for the new target in the X-Y stores 31 and 37, the observer simply throws the manual Switch 104 to the store position A and depresses the Vpush-button switch 320, thereby connecting` the coordinate resolver 93 to the X-Y stores 31 and 37 through the store contacts 102; When theproper voltages have been inserted, the operator releases the push-button 320 and moves the switch 104 to its neutral position -B.

Of course, thereis a lamp, a manual switch, coincidence circuit'and rectifier-filter circuit for each set` of stores. Referring to Figure 7, the input signals from the pulse former 13`a nd the X-Y comparator 21 are impressed (Figure 6).

4'upon input resistors 125 and 126'in the coincidence Acircuit 98. The valuesof these resistors -125 and 126 are smallcompared with that of the series resistor 127 so that the appearance of a pulse vacross only one input resistor, for example 125,rresults in a rather smalloutput, due to the fact that the other resistor 12,6 audits associated -rectiier 131 constitute a low impedance parallel path.-

If the input pulses occur simultaneously, however, a j

relatively large output pulse Ais obtained. The output pulse is then rectilied and iiltered by means of a rectifier 128 and a resistor-capacitor lter network 129--130, the rectied and filtered output lbeing applied to the lamp 101 through the sampler 94Vand the amplifier 100 What is claimed is:

1. In a display system, in combination, a irst display device responsiveto applied voltages for displaying indications; a second display. device responsiveto vapplied .voltages for displaying indications; means Afor producing voltages 4indicative of the position on one of said display devices of at leastsome of the indications thereon; means 'coupled'to said other display device and responsive to.

said produced voltages for placing indications on said other display device in the same relative positions as said some indications onsaid one display device; and means Voperatively associated with said two display devices for distinguishing the indications on one device duplicated on the other from those on said one device not duplicated on the other. Y 2. In a display system,'in combination, a iirst display device responsive to applied` voltages for displaying indivcations; a second display device responsive to4 applied voltages for displaying indications; means operatively associated with twordisplay devices forbproducingaY .on said onedisplay device; Vand means operatively associated withl said two devices,Y for distinguishing a combined indicationy of superimposed indications from a combined indication of non-superimposed indications'.

3. In a` display system, in combination, Va iirst display device responsive to applied voltages for displaying indifcations; Va second display device responsiveto applied voltages for displaying indications; means operatively associatedwith two display devices'forrproducing a combined indication of the indications on isaid two devices, with indications in the same relative positions onthe two devices superimposed; means for producing voltages indicative of the position on one of said display devices of at least one of the indications thereon; means coupled to said other display device and responsive to said pro-4 duced voltage for placing an indication on said other display device in a'position corresponding to the position of said indication on said one display device; and means operatively associated with said two. devices for distinguishing a combined indication of superimposed indications from a combined indication'of non-superimposed indications. Y 4. In a display system as set forth in claim 3, said two display devices comprising cathode ray tube indicators having screens of the same size and Shaper Y l Y 5. In a radar system, in combination, a first. circuitfor detecting signals corresponding to all objects within the range-of said system; display meansv coupledto'saidA circuit for displaying said signals infpositions corresponding to the positions ,inl space ofV said objects; means for deriving from some of, said signals analog voltages indic- `12 ative of the positions fin space of said objects; s tor`age means lcoupled -to said last-named means Vfor .indivldually ,storing said analog'voltages; and display means coupled i to said rstorage means for displaying the-stored voltages in positions corresponding to the positions in spaceof the objects to which said stored vvoltages correspond.; i;

l6. In a radar system, in combination,Y arstlciicuit for detecting signals corresponding -toall objectsfawithiiztv the range Aof said system; cathode rayV tube Vdisplay means coupled to said circuit for displaying said'signals in positions corresponding to the'positions in space of said objects; means for deriving from some of said signals analog voltages indicative of the positions in space of said objects; storage means coupled to said last-named means for individually storing said analog voltages; and ,cathodev ray tube display means coupled to` said Ystorage means for displaying thestored Vvoltages' vin' positions corresponding'to the positions in space of the objects to which said stored voltages correspond- Y 7. In a radar system, in combination, a

circuit for displaying said signals inpositions correspond-Y ing to'the positions in space of said objects; meansf f or deriving from atleast some of said signals analog voltages means for individually storing, said Yanalog"voltages';

second display means coupled to'v saidstorage means-for first-circuit,V- i for detecting signalsv corresponding'to all ohjectsQwithin the range of said systemdisplay means coupledtofsaid g indicative of the positions in` spaceoffsaid.Y objects;` agi@ c plurality of storage means coupled vto said'last-named displaying the'stored voltages infpositions corresponding to the positionslin space of theobjec'tsxto which said I l Vstored voltages correspond; andimeans coupled to at least oneof said A storage means and to said-seconddisplay means for generatingV atleast one analog voltage indicai l tive of a position inspaceand 'supplyingthe same to said one storage means, and' simultaneously placing a signal on said second display means in a position indicativeof 'Y said position in space. 8. In a radarsystem, in combination, a first circuit for detecting signals correspondingto all objects 'within' the range of said system; display meansY coupled to said circuit for displaying said signals in positions correspond;V ing tothe positions in space of said objects; means Vfor deriving from someof saidsign'als analog voltages'indicative of the positions in .space of said objects; "storage means coupled to said last-named means forV individually Y storing said analog voltages; display means coupled to 'saidstorage meansY for displaying the stored voltages in positions Ycorresponding tothe positions Vin space ofthe objects ;to which said stored voltages correspond; and means operatively associated with said two display means for producing a combined display of the signals onsaid on said two display means superimposed.V Y

two means with indications in the same relative positions 9. In a radar system, in combination, a iirst circuitrfor detecting signals corresponding to all objects within the' range of'said system; display means coupled to said circuit for displaying said signals in positions corresponding to the positions in space of said objects; means for deriving from some of said signals'analog voltagesV indicative Vof the positions in space of said objects;"a plurality `of storage means coupled to' said last-named means foi individually storing said analog voltages; second display means coupled to said storage means for displaying the stored voltages in positions corresponding to the positions in space of the objects to which said stored voltages correspond; means coupled to at least-one'of said storage means and to said second display means for generating at least one analog voltage indicative `of a position in space and supplying the same to said one storage means,

and simultaneously placing a signal on saidsecon-d displayV means'iuV a position indicative of said position in space;

and means operatively associated with said two display means for distinguishing the signals'which are inthe same j geraete for deriving from said signals analog voltages indicativeV of the positions in space of theV objects from which the storing voltages derived from at least one of said signals, in combination, second display means responsive to voltages for displaying signals in positions corresponding to the positions in. space to which said voltages correspond; and voltage generator means coupled to at least one of said storage means and to said second display means for generating at least one analog voltage indicative of a position in space and supplying the same to said one storage means, and simultaneously placing a signal on said second display means in a position indicative of said position in space. i 1f 11. In a radarsystem as set forth in claim l0, further including means operatively associated with said two display means for distinguishing thelsignals on the iirst and second means which. are inthe same relative positions on said two means from thosenot in the same relative positions on said two means. i

l2. In aradar system as set forth in claim ll, said two display means comprising cathode ray tube indicators.

13. In a radar system including circuit means for receiving signals from objects within the range of said system, means for deriving from at least some of said signals analog voltages indicative of the positions in space of the objects from which the signals are received, storage means for storing the analog voltages derivedgfrom one of said signals, and means responsiveto a stored analog `signals arereceived, and storage means for individually Y ing echoes from said objects, in combination, first display means for displaying said echoes in positions correspond- `ing to the positions in space of theobjects from which the echoes are received; second display means responsive to a generated voltage for producing indications; selection means for generating a voltagand applying the same 'to said second display means for producing an indication on said second `display means `in the same relative position as a given echo on said first display means; and means operatively associated with said two display means for producing a combined indication of said-two display means with indications of one superimposed on corresponding indications ofthe other.

16. Apparatus in accordance with claim 15, whereinY said display means comprise cathode ray rube indicators, and said means for producing a combined indication cornprises a dichroic mirror arranged to reflect `light from the screen of one of the indicators and to transmit light Y Tfronrthe screen of the other indicator.

17. Ina display system, .-incombination,` 'a iirst display device responsive t0 ,applied voltagesfor displaying first voltage and to said signals for periodically correcting that `voltage as the object from which the voltage his derived moves in space, an arrangement for` selecting for storage in said` storage means the analog voltages indicative of a particular object comprising, in combination, first means receptive of said signals for producing visual indicia thereof in positions corresponding to the positions in space of the objects from whichv they are received;

second means receptive of a generated voltage for prol 4 ducing a visual indicium thereof; voltage generating means coupled to said storage means and to said second means for producing a visual indiciumV on said' second means in a position corresponding to` that of a position in `space and simultaneously inserting in said storage l means an analog voltage indicative of "said position in space; and means for viewing the visual indicia'lo'n said iirst means and the visual indicium on said second means in superimposed relation.

indications, a second display device responsive to applied voltages for Vdisplaying second indications, optical means operatively associated with said` display devices for characteristically diierentiating said rstfindications from said second indications and for superposing said diierentiated second indications on correspondingly` located, ditferentiated `irst indications, means for Ygenerating voltages indicative of the positions of indications Aon said first display device,` and utilization means coupledgto said second display device and responsive to said` generated voltages for producing indications on said second display device.

18,. Apparatus in accordancewith claim 17, wherein said `display devices-comprise cathode-ray display tubes e and said optical means comprises-a dichroic mirror.

' 1S. In alradar system includingmeans for transmitting Ypulses to targetsV in an, area, meansfor receiving echo 'pulses reiiected from said targets and iirst indicating means for displaying said echoes, in combination, means for deriving from at least one of said received echoesa given pair of coordinate voltages indicative of the posi- Ation in space relative. to` said transmittnglmeansofthe target@ from which said one echo is retlected; a plurality of pairs` of storage' cir cuits,` each said pair including one storage circuit for'storing one coordinate voltage of `a pair of said voltagesand another storage circuit` forV stor-VV ing the other coordinate voltage offsaid pairlof coordinater;1voltages'; second indicating vmeans including means for producing agsimulated echo thereon and deiiection means I respofnsive. to"` a pairv of coordinate voltages for adjusting the position on" said second indicating means offsaid simulatedecho to correspond to the position on 14. A radar system including circuit `means for'` receiv;

ing signals from objects within the range of said system; means for deriving from at least some of said signals analog voltages indicative of the positions in space of the objects from which the signals are received; storage means for individually storing the analog voltages derived from at least some of said signals; means responsive to a stored analog voltage and to said signals for periodically correcting that voltage as the object from which the voltage is derived moves in space; irst means receptive of said signals for producing visual indicia thereof in positions corresponding to the positions in space of the objects from which they are received; second means coupled to said storage means for producing visual indicia in positions corresponding to the positions in space of the objects to which the stored analog voltages correspond; and means for distinguishing the visual indicia on said first and second means which are in the same relative positions on said two means from thoseV not inthe same relative positions on said two means.

l5. In a radar system including means for transmitting pulses to objects in a predetermined area and for receivsaid iirst indicating means of anp-echo from` which is;

' deriveda pair of coordinate voltagesrof thesame value; i i i vadjustable circuit means for producing a pair of coordinate voltages indicative of the position in space of any target; switch means for connecting Ysaid adjustable circuit means to said second indicating means for deflect- Ving the simulated echo thereon in accordance with the coordinate voltages produced by said adjustable circuit means, and for connecting said adjustable circuit means to a selected pair of said` storage circuits so asV to charge said selected pair of saidrstorage circuits to apair of coordinate voltages produced by said adjustable circuit means; means for adjusting said circuit means to produce a pair of coordinate voltages of the same amplitude as said given pair of` coordinate voltages, whereby said simulated echo is moved to a position on said second indicating means corresponding to the position of Said one echo on said first indicating means; and comparison means connected intermediate said selected pair of storage circuits and said means for deriving from said one received echo a pair of coordinate voltages for comparing the voltage stored in said pair of selected storage circuits and said given pair of coordinate voltages and when they 'are within a predetermined range with respect to each other forchanging the voltage stored in said selected pair' of storage circuits` in accordance with any changes in said givenv pairy of coordinate y voltages.

20. In' a radar' system as set forth in' claim* 19, furlther including fmea'ns for Asuperimposing the 'display on lsaid'lirst indicatingmeans on the displayo-nsaid second indicating means with Aechoes on 'one superimposed `on corresponding echoes lori-the other including means for distinguishing superimposed indications from non-super'- `imposedindications.` f

2l. lIn a radar system as set forth in claim 19, each said indicating means including -a screen and said two -screens bein'gperpendicularly disposed with respect to one another, and further including a dichroic element positioned at an'an'gle' of'45 with each screen for permitting light vfromone said screen to passthrouglr said lelement `,and light from the otherl said screen to be re flected from said elementjsaidscreens lbeing positioned 'relative 'to one" another lsoV lthatimages in corresponding places, fon1 said screensf arev superimposed.`

22. lApparatus inA accordance with claim? 20, wherein said adjustable circuit-means comprises a joystick mechanism comprising 'ai lever coupled -toV two orthogonally Y.disposed shafts and movable in two orthogonalY planes, a separatefpotentiometer associated with each shaft, each 4ofsaid potentiometers-having its contact Aarm coupled to .'lthe' shaft with which said potentiometer is associated,'a fdirectcurrent, signal -s'ourcercoupled to eachlof said p oitentiome'ters, and vmeans for deriving a direct-current Asignalfrom eachcfffsaid `potentiometers in accordance with the positionof said lever.A Y 23.Apparatus-in accordance with clairn'ZO, wherein Vsaid adjustable'circuitVrneans'comprises'a joystick mechanism comprising-a'elever coupled to twoorthogonallyY disposed Shafts and movable in two orthogonal planes, a f separate y synchro associated v withA eachY of said shafts, Land means forf deriving a direct-currentsi-gnal from' feach synchro in accordance-with the position of said llever.A l v 124. In a radar system as set forth in"c1aim`l.9,vfurther Y including a plurality of indicating devices, one operative- `ly` associated ,with each pair of storage circuits, for in'- fdicating when-each pair of storage circuits hasa pair of "cliarges corresponding to fa'pair-"of coordinate voltages 's toredthe'rein. i; n Y

25. Ina radar set as set forth in'claim 24, saidindicating 'devices` including lindicating lights," one -lightlbeing associated vwith each'pair of storage circuits.,

26, 'Ina radarha'ving 'means for tia'nsmi'ttingpnlses -to'targets in an area, Ameans for receiving echo signals reected from said targets, means for deriving from said received echoes sets of rst electrical analog signals indicative of the spatial position of thetarget'sifr'orh which-said echoes are reflected, said sets of analog signals being 'periodically derived anew for each target from' which echo signals are being received, means for storing Yat least one ot said sets of analog signals, and means for Vcorrecting each stored set of analog signalsin accordance with the newly derived analog signals forfthetar'get from which the stored analog signals were previously derived, means for indicating targets whosepanalo'g signalsV 'are not being stored comprislngin combination, a radar displayv device coupled to said receiving means for `displaying saidecho signals, a resolving means for producing' sets of second signals indicative ofthe spatial posi- -tion of a -target corresponding to Vanyfecho displayed on said first display means, a monitor display device coupled t o said resolving means Yfor displaying said sets of second signals, and dichroic means operatively associated with vsaidfdisplay device for transmitted light of one color and retlectedlight of a diierent color, said dichroic means being optically arranged to transmit the indication from vone device, reflect 'the indications from the other device and Vsuperimposed said -reected'and transmitted indications to form a combined indication. Y

27. In aradar having means for transmitting pulses to. targetsin anarea, means for receiving echoes from said targets and displaying them on an echo indicating device, and sets of circuit means for periodicallyderiv'- ing and storing sets of first electricalanalog signals indicative of the spatial positions of selected targets'whose, I' echoes are being received, means for visually indicatingv those tar-gets whose analog signals are being stored, comprising, in combination resolvingvmeans for producing i from said 4displayed echoes sets of second electrical ana"- log signals indicative of the spatial positions of'thertargets from which said,A displayed echoes' are reected, Vmonitor' display means for displaying said sets of second analog signals, and optical means for producing 'a combined indication yof said echo and` monitorV displaysV Y wherein corresponding indications aresuperimposed and Y 2,548,900 Lester L Apr.17, ,1951 

